US1686876A - Method of manufacturing magnesite brick - Google Patents

Description

Pa es oer. 9, 1 928.

UNITED STATES PATENT 'orFIcE'.

BERRY MARVEL OHARRA, OI WESTFIELD, AND EDGAR A. SIIAGIIE, 01 TRENTON, NEW JERSEY, ASSIGNORS '10 AMERICAN SMEL'IING AND DEFINING COMPANY, 01' NEW YORK, N. Y., A CORYORATION Q1 NEW JERSEY. 7

METHOD OF MANUFACTURING IAGHQESITE BRICK.

No Drawing.

This invention relates broadly to. the method of making refractories for use in metallurgical furnaces, and more particularly to magnesite brick having exceptionally high resistance to the corrosive action of metallurgical slags at the high temperatures 'atwhich metallurgical operations may be prac ticed.

The invention relates further to the method of making magnesite brick which is composed almost entirely of pure magnesium oxide and which therefore is free from iron or other elements which would be readily attacked andcorroded by the slags to which said brick may be exposed in use. It also relates to magnesite brick having a dense structure, and mechanical strength such that it will not be distorted or destroyed by the mechanical load to which it may be subjected in use in the furnace. The invention also relates to a method for manufacturing magnesite brick, whereby a strong, dense corrosion resistant brick may be produced.

The invention further consistsin the new and novel features of operation and the new and original arrangements and combi-' nation of steps in the process hereinafter described, and more particularly set forth in the claims.

The invention also consists in forming a product having the general characteristics, the new and useful application, and the several original features of utility herein after set forth and claimed.

Magnesite brick as ordinarily produced at resent'are made from calcined magnesite whlch contains naturally, or to which are added, certain agents the purpose of which is to form chemical compounds which bind together the particles of magnesium oxide, and give suflicient strength to the brick to enable it to support the loads to which it may be subjected in'use. Ferric oxide, in amounts up to 7 per cent or more of the magnesite, is the agent most generally used, although other binders such as clay, sodium silicate, and the like, have been suggested. When bricks made from such mixtures are burned, during the process of manufacture the iron oxide, or other binder, unites with a portion of the magnesium oxide to form ferro-magnesian. or similar compounds, which are more readily Application fled September 17, 198. Serial No 136,208.

fusible than the magnesium oxide andwhich consequently part1 fuse or sinter, thereby forming a bond magnesium oxide. The brick produced as a result of this action is dense and of considerable strength, but of only moderately high refractoriness. Inuse, when such brick are exposed to the action of corrosive slags at high'temperatures, for'example, as when they are used for lining reverberatory furnaces for smelting copper ores, they are rapidly corroded-by the slag and must soon be replaced. Microscopic examination of such brick, after they have been in use, shows that the corrosion has been caused by the chemical action of the slag upon the ferromagnesian or other compounds, making up the binder, and that'the particles of magnesium oxide are not themselves greatly at-v tacked chemically by the slag, but are carried away mechanically, after the binder,

which should have held them together, has

been destroyed. It has been suggested to make a brick of much purer calcined magnesite to avoid-this difiiculty, but all such brick heretofore made have been so weak mechanically, due to the absence of any compound to serve as a binder for the particles of magnesite, that they fail in use for lack of mechanical strength.

By the herein disclosed invention it is possible to manufacture brick. which consists almost entirely. of pure magnesium' oxide, which. hasv a dense structure, which is strong mechanically and which at the same time has extremely high resistance to the action of corrosive slags at high temperatures. 'This brick consists of particles of calcined magnesite or magnesia as free as possible'from ferric oxide or other impurities. which are held together by means of colloidal or very finely divided magnesium oxide. and which may be burned for a sufficient length of time to convert a substantial portion of the magnesium oxide to the mineral periclase.

One meth d by which this invention may be racticed is as .follows:

I s raw material, comparatively ure calcined ma'gnesite, as free as ossi 1e from ferric oxide or other impurities, may, be selected; Thismagnesite ma first be crushed to whatever size may preferably being crushed rather fine. as n etween the particles of desired,

this ure calcined magnesitemay now be mix colloidal or semi-colloidal magnesium mfe hydroxide, and suilicient water to give the 5 mixture the proper consistency to be pressed intoimolds. a

The colloidal or semi-colloidal ma esmm' droxide" is an exceptionally. goo binder while the bricks are in the green or unburned 10 state. When heated, in burning the bricks, it ives off water and becomes converted to col oidal or semi-colloidal magnesium oxide, which, in turn, serves as an excellent binder for the brick in the burned .statc. B continuing'the burning operation for a s c1ent length of time at the usual temperature of burning magnesite bricks, or at a somewhat higher temperature for a shorter length of time, the magnesium. oxide may be partially olr ,wholly converted into the mineral penase.

Preferably, suflicient magnesium hgdroxide may be used to coat or surroun each article of the calcined magnesia with a thin lm of the colloidal or semi-colloidal magnesium hydroxide. The quantity most sultable varies, of course, with the size and eral character of the calcined magnesia, ut, by way of illustration, it may be stated that so 5 to 10 per cent of colloidal magnesium hydroxide has been found suitable with a certain calcined magnesite.

The mixture of calcined ma esite, colloidal magnesium hydroxide an water may 5 now be molded into bricks, preferabl under high pressure in order to compress t e mixture as much as ossible, and may then be. dried and burned in an suitable form of kiln at thetemperature esired. The burning temperature may preferably be about cone 16 or higher, and may be continued for a suflicient length of time to convert a substantial amount or all of the magnesium oxide both that in the binder and that in the particles of calcined magnesite, into the mineral periclase. 7

By this procedure each brick becomes practically a solid block of periclase and is exceedingly resistant to the action of the most corrosive slags, even, those of a fer ruginous nature, as well as being exceptionally dense and strong.

The colloidal or semi-colloidal magnesium hydroxide to be mixed with the'particles of calcined magnesite may be produced mechanically by comminuting crystalline magnesium oxide to an exceedingly fine or ultramicroscopic size, and emulsifying the product in water. It'may also be produced by chemical means such as by mixing together solutions,-.o ne 0 which may be a solution of a soluble magnesium salt, such as magnesium chloride, and the other a solution containing ap roximately an equivalent amount of a so uble alkali-,such as sodiumhydroxide or ammonium h droxid'e. The magnesium hywashed to rid it of salts, such as so. ium Y chloride, formed when. it is precipitated, or

it may be precipitated directly 1n.contact with the particles of calcined ma esite. H the latter method of preparing t e colloidal magnesium hydroxide is to be used, the calcined magneslte may first be wet with a small ampunt of water containin desired amount of the so uble magnesium in solution the.

salt. To this mixture may then be added a I water solution of the soluble alkali, cont ining an amount of the alkali approximate y equivalent to the amount of soluble ma nesium salt used. The whole may then fie thoroughly mixed, during which mixing the soluble magnesium salt and the alkali react to form magnesium h droxide, which is precipitated as a. colloidal, 'elly-like film around each individual partic eaof calcined magnesite.

The brick made by this' method contain practicall no impurities; hence, they are exceptional y resistant-to the corrosive action of slags, even at the hi hest temperature to which they may be an jected in use. The colloidal magnesia makes a firm binder to unite the coarser articles of magnesite, so that the brick is ense and strong mechanically as well as chemically.

it is obvious that the advantages of this material, in which calcined magnesite is bonded b means of very finely comminuted or colloi al magnesium oxide are not confined to magnes1te bricks, but that it may also be used in other forms. For example, the mixture of calcined magnesite and colloidal magnesium hydroxide may be tamped into place as in a furnace bottom, and there be burned in place to convert the magnesium hydroxide to magnesium oxide, thereby to secure the bonding of the calcined magnesite.

This new product, on account of its purity, its denseness and its mechanical strength, 1s a highly superior refractory for use under any conditions in which it may be desirable to employ magnesite brick. In consequence of its great resistance to corrosion, both that due to chemical action and that due to mechanical causes, furnace linings or other objects made of this brick have a much longer life than those made of the ordinary magnesite brick. Therefore, great savings m metallurgical operations are made possible,

since the furnaces or other apparatus in which this new material is employed will last much longer than heretofore before expensive repairs or renewals become necessary, and the cost per ton of metal or other product roduced 1n the furnace is thereby material y decreased.

The process by which this new magnesite brickmay be manufactured is remarkably simple to practice, and-requires no complicated machinery or operations. It may be carried on at any plant having the ordinary apparatus for making refractories, as the colloidal magnesium hydroxide is not difiicult to prepare and may readily be mixed with the calcined magnesite in the commonly used types of mixers. I

Although one process for producing this improved product has been set forth and described, it is obvious that various omissions, substitutions and changes may be made in the process or in the separate steps thereof without departing from the spirit of the invention and without modifying or changing the essential features and characteristics of the product produced, and that such product remains substantially the same although slight modifications may be made in its appearance and texture, and in its physical and chemical characteristics.

What is claimed is:

1. Process of manufacturing magnesite brick which consists in crushing calcined magnesite into small particles, mixing with said particles water containing magnesium chloride in amount equivalent to 5 to 10 percent of the calcined magnesite, addin to said mixture an aqueous solution of sodlum hydroxide or ammonium hydroxide in amount approximately e uivalent to the magnesium chloride, there y to form magnesium hydroxide in contact with the particles of magnesite, compressin ture into bricks, burning the bric s, whereby the magnesium hydroxide is converted to magnesium oxide, and continuing the burning at a higher temperature to convert the magnesium oxide into periclase.

2. Process ofmanufacturing magnesite brick which consists in crushing calcined magnesite into small particles, mlxing with the mix:

said particles water containing a small roportion ofa soluble magnesium salt, ad ing to said mixture an aqueous solution of soluble alkali in amount substantially equivalent to the dissolved magnesium salt, thereby to form a small proportion of magnesium hydroxide in contact with the particles of magnesite, compressing the mixture into bricks, burning the bricks whereby the magnesium hydroxide is converted to magnesium oxide, and continuing the burning at a higher temperature to convert the magnesium oxide into periclase.

3. Process of manufacturing magnesite brick which-consists in mixing with small particles of calcined magnesite water containing a small proportion of soluble magnesium salt, adding to said mixture an aqueous solution of soluble alkali in amount approximately equivalent to the dissolved magnesium salt, thereby to form a small proportion of magnesium hydroxide in contact with the particles of calcined magnesite, compressing the mixture into bricks and burning the bricks, whereby the magnesium hydroxide is converted 'to magnesium oxide.

4. The rocess of manufacturing magnesite bric which comprises crushing calcined magnesite into small particles, mixing therewith asmall proportion of colloidal magnesium hydroxide for forming a temporar binder for the plastic mass, forming the mixture to bricks and burning the bricks to convert the colloidal magnesium hydroxide into colloidal magnesium oxide, said oxide-forming a permanent binder for the bricks.

In testimony whereof we have hereunto set our hands.

,BERRY MARVEL OHARRA.

EDGAR A. SLAGLE.